Yarn withdrawal nozzles can be secured replaceably for example in a so-called channel plate adapter of a cover element closing the open-end rotor spinning machine during the spinning operation. As the yarn withdrawal nozzles are subject to heavy wear from the running yarn, they usually consist of a funnel-like nozzle insert which is made from a very wear-resistant material, preferably a technical ceramic material, and is secured permanently in a nozzle fitting made from a metal material, for example by an adhesive or press-fitting connection.
The channel plate adapter consists essentially of a preferably circular basic body with a rear, conically designed bearing surface and an outlet part which projects during the spinning operation into the spinning rotor and the dimensions of which are adjusted to a specific spinning rotor diameter or diameter range.
The outlet area of a so-called fiber guiding channel is also formed in said outlet part of the channel plate adapter.
Such channel plate adapters have a central through bore, in which on the input side the yarn withdrawal nozzle is secured replaceably and in which on the outlet side a so-called yarn take-off tube engages.
The yarn withdrawal nozzle secured replaceably in the central through bore of a channel plate adapter generally consists, as shown for example in German Patent Publication DE 10 2008 019 214 A1, of a special nozzle fitting and a ceramic nozzle insert secured permanently onto the nozzle fitting.
The generally ferromagnetic nozzle setting corresponds with corresponding permanent magnets embedded in the channel plate adapter, which secure them in a force-fitting manner.
Such yarn withdrawal nozzles that have been known for a long time have proved effective in practice and make it possible to create optimal spinning conditions in open-end spinning devices.
The disadvantage of these yarn withdrawal nozzles is however that they are very expensive to manufacture and thus have a relatively high cost. For example the configuration of the transition from the nozzle insert to the nozzle setting is particularly complex to avoid the formation of any welt edges which would have a negative effect on the quality of the yarn because of the additional friction. Owing to the fit of the nozzle insert and nozzle setting in addition only small deviations are permissible in manufacturing which results in high production costs caused by rejects or the post-processing of parts.
Additional magnetically fixable yarn withdrawal nozzles are disclosed for example by German Patent Publications DE 27 45 195 A1, DE 37 29 425 A1 or DE 195 02 917 A1.
As shown in particular in German Patent Publication DE 27 45 195 A1, such a yarn withdrawal nozzle is made either of ferromagnetic material or a ceramic material with a ferromagnetic ring.
The yarn withdrawal nozzle according to German Patent Publication DE 37 29 425 A1 is also made of ceramic material and has a ferromagnetic disc which corresponds with a magnetic ring disc which is attached to the holder. In order that the fiber feed channel can be guided past the magnetic ring disc is missing a sector of about 60°.
The disadvantage of the yarn withdrawal nozzles according to German Patent Publications DE 27 45 195 A1 or DE 37 29 425 A1 is that no anti-rotation device is provided for the yarn withdrawal nozzle in the holder. This can mean, particularly with difficult yarns, that the magnetic fixing of the yarn withdrawal nozzle is not sufficient and the yarn withdrawal nozzle co-rotates in its holder which has a negative effect on the forming yarn.
From German Patent Publication DE 195 02 917 A1 therefore a yarn withdrawal nozzle is disclosed which in addition to the magnetic coupling ensures a desired installation position and also facilitates the release of the magnetic coupling.
In addition, the yarn withdrawal nozzle comprises a positioning means which in a different installation position of the yarn withdrawal nozzle than the one intended weakens the magnetic effect on the bearing surface at least. This is achieved in that the positioning means contains a cam-like catch securing the installation position which can be inserted into a recess of the holder.
To facilitate the release of the magnetic coupling, in addition a so-called uncoupling device is disclosed which is formed either by a recess provided in the bearing surface or by a support surface lifting the bearing surface from the holder. Said uncoupling devices have a lifting or weakening effect on the magnetism so that the yarn withdrawal nozzle can be disassembled more easily.
By using yarn withdrawal nozzles according to German Patent Publication DE 195 02 917 A1 an anti-rotational securing of the yarn withdrawal nozzle is ensured in its holder, but only with a very specific configuration of the yarn withdrawal nozzle and a very specific installation position. In addition, such yarn withdrawal nozzles are expensive to manufacture. A tool is generally necessary for the installation and disassembly in order to lock the yarn withdrawal nozzle to be used or in order to release the engaged yarn withdrawal nozzle.